The present invention relates in general to anti-cancer agents and more specifically to synthetic analogs of the antimitotic marine natural product curacin A.
Natural products remain a significant source of promising lead structures for drug development. Cragg, G. M.; Newman, D. J.; Snader, K. M. J. Nat. Prod. 1997, 60, 52; Shu, Y.-Z. J. Nat. Prod. 1998, 61, 1053; Nicolaou, K. C.; Vourloumis, D.; Winssinger, N.; Baran, P. S. Angew. Chem., Int. Ed. 2000, 39, 44. In recent years, an expansion of the structural diversity pool by preparation of libraries of natural products or natural product-like molecules has become a major focus of combinatorial chemistry. Tan, D. S.; Foley, M. A.; Shair, M. D.; Schreiber, S. L. J. Am. Chem. Soc. 1998, 120, 8565; Nicolaou, K. C.; Winssinger, N.; Vourloumis, D.; Oshima, T.; Kim, S.; Pfeffeirkorn, J.; Xu, J.-Y.; Li, T. J. Am. Chem. Soc. 1998, 120, 10814; Meseguer, B.; Alonso-Diaz, D.; Griebenow, N.; Herget, T.; Waldmann, H. Angew. Chem., Int. Engl. 1999, 19, 2902. After completion of the total synthesis of the strongly antimitotic Lyngbya majuscula metabolite curacin A in 1996 (Wipf, P.; Xu, W. J. Org. Chem. 1996, 61, 6556), the inventors remained intrigued by the impressive antiproliferative profile (Verdier-Pinard, P.; Sitachitta, M.; Rossi, J. V.; Sackett, D. L.; Gerwick, W. H.; Hamel, E. Arch. Biochem. Biophys. 1999, 370, 51; Gerwick, W. H.; Protear, P. J.; Nagle, D. G.; Hamel, E.; Blokhin, A.; Slate, D. J. Org. Chem. 1994, 59, 1243) of this marine natural product and its potential use as a lead structure for the development of new synthetic tubulin polymerization inhibitors. For a review of agents that interact with the mitotic spindle, see: Jordan, A.; Hadfield, J. A.; Lawrence, N. J.; McGown, A. T. Med. Res. Rev. 1998, 18, 259-69. For recent evaluations of small-molecule antimitotic agents, see: Haggarty, S. J.; Mayer, T. U.; Miyamoto, D. T.; Fathi, R.; King, R. W.; Mitchison, T. J.; Schreiber, S. L. Chem. Biol. 2000, 7, 275; Owa, T.; Okauchi, T.; Yoshimasa, K.; Sugi, N. H.; Ozawa, Y.; Nagasu, T.; Koyanagi, N.; Okabe, T.; Kitoh, K.; Yoshino, H. Bioorg. Med. Chem. Lett. 2000, 10, 1223; Uckun, F. M.; Mao, C.; Vassilev, A. O.; Navara, C. S.; Narla, K. S.; Jan, S.-T. Bioorg. Med. Chem. Lett. 2000, 10, 1015.
Compounds that inhibit cell proliferation are potentially useful in treating cancer, among other diseases. Curacin A is one such compound that inhibits cell growth and mitosis. See U.S. Pat. Nos. 6,057,348 and 5,324,739. Curacin A is believed to act by inhibiting microtubule processes associated with cell replication. It does this by binding to the colchicine-binding site, which is a relatively unique drug binding site.
Microtubules, the GTP hydrolysis-induced macromolecular assembly of xcex1/xcex2 tubulin heterodimers, are an indispensable cytoskeletal component. Intracellular microtubule arrays serve as the scaffold for support of the endoplasmic reticulum and as the railway by which organelles and vesicles are delivered by motor proteins in interphase cells. Mitosis is a four-stage process of cell division resulting in the production two identical daughter cells from a single parent cell. Not only are the daughter cells identical to each other, they are identical to the parent cell.
At mitosis, microtubules also serve as the cables through which force generated by motor proteins causes sister chromatids to segregate. Agents that alter the formation, stability and/or disassembly of microtubules typically arrest cell growth at the G2/M interface of the cell cycle, and may therefore be useful as antitumor agents. There are three major drug-interactive sites on tubulin. Two of these are the basis of clinically useful antitumor agents. The paclitaxel site on xcex2-tubulin is bound by paclitaxel and docetaxel, which stabilize microtubules against disassembly. The vinca domain, bound by agents such as vinblastine, vincristine and vinflurabine, which inhibit proper assembly of tubulin heterodimers into microtubules, is at an incompletely elucidated region of the heterodimer.
A third major class of microtubule perturbing agents bind to the colchicine site, which appears to be largely or exclusively on xcex2-tubulin, but may include regions of the xcex1/xcex2 interface. Agents that bind to the colchicine site appear to have affinity for unassembled xcex1/xcex2 heterodimers. Until recently, all agents with known affinity for the colchicine site could be described as biaryl systems with appropriate substituents linked by short alkyl/alkenyl chains. The only useful pharmacological actions of colchicine site agents have been in the treatment of inflammatory processes. Discovery of the antitumor and associated antiangiogenesis actions in animal models of some colchicine site agents (e.g. 2-methoxyestradiol, combretastatin A-4 phosphate) suggest, however, that perturbation via this domain may yet prove useful for cancer treatment.
The discovery that curacin A and some of its closely related analogs bind the colchicine site with high avidity and are potent antimitotic agents caused a reevaluation of the biaryl systems theory. Early structure-activity relationship studies with curacins indicate that the parent structure is very intolerant of modification.
Curacin A exhibits anticancer properties similar to paclitaxel. Like paclitaxel, curacin A comes from a natural source. Both compounds exhibit a remarkable ability to disrupt cell mitosis, thereby inhibiting cell proliferation. This antimitotic ability makes these compounds potentially promising in treating cancer. In the case of both paclitaxel and curacin A, the trend is towards developing methods of synthesizing analogs that exhibit greater biological activity than the naturally derived compounds. Additionally, these methods should be more efficient than deriving the compounds from natural sources. As such, it is highly desirable to find ways of synthesizing more stable and biologically active analogs of curacin A.
According to several reports, curacin A promotes arrest of the cell cycle at the G2/M checkpoint and competitively inhibits the binding of [3H]-colchicine to tubulin, and it can therefore be considered a colchicine site agent. Jordan, A.; Hadfield, J. A.; Lawrence, N. J.; McGown, A. T. Med. Res. Rev. 1998, 18, 259-69; Verdier-Pinard, P.; Lai, J.-Y.; Yoo, H.-D.; Yu, J.; Marquez, B.; Nagle, D. G.; Nambu, M.; White, J. D.; Falck, J. R.; Gerwick, W. H.; Day, B. W.; Hamel, E. Mol. Pharmacol. 1998, 53, 62. In addition to a large number of total syntheses of curacin A, the attractive biological properties of this compound have led to numerous biological studies. For discussion of curacin A syntheses, see: White, J. D.; Kim, T.-S.; Nambu, M. J. Am. Chem. Soc. 1995, 117, 5612; Hoemann, M. Z.; Agrios, K. A.; Aube, J. Tetrahedron Lett. 1996, 37, 935; Ito, H.; Imai, N.; Takao, K.; Kobayashi, S. Tetrahedron Lett. 1996, 37, 1799; Onada, T.; Shirai, R.; Koiso, Y.; Iwasaki, S. Tetrahedron Lett. 1996, 37, 4397; Lai, J.-Y.; Yu, J.; Mekonnen, B.; Falck, J. R. Tetrahedron Lett. 1996, 37, 7167; White, J. D.; Kim., T.-S.; Nambu, M. J. Am. Chem. Soc. 1997, 119, 103; Hoemann, M. Z.; Agrios, K. A.; Aube, J. Tetrahedron 1997, 53, 11087; Muir, J. C.; Pattenden, G.; Ye, T. Tetrahedron Lett. 1998, 39, 2861. However, even minor changes in the structure of curacin A can lead to essentially inactive derivatives. Verdier-Pinard, P.; Lai, J.-Y.; Yoo, H.-D.; Yu, J.; Marquez, B.; Nagle, D. G.; Nambu, M.; White, J. D.; Falck, J. R.; Gerwiek, W. H.; Day, B. W.; Hamel, E. Mol. Pharmacol. 1998, 53, 62; Marquez, B.; Verdier-Pinard, P.; Hamel, E.; Gerwick, W. H. Phytochemistry, 1998, 49, 2387; Nishikawa, A.; Shirai, R.; Koiso, Y.; Hashimoto, Y.; Iwasaki, S. Bioorg. Med. Chem. Lett. 1997, 7, 2657; Martin, B. K. D.; Mann, J.; Sageot, O. A. J. Chem. Soc., Perkin Trans. 1, 1999, 2455; Onoda, T.; Shirai, R.; Koiso, Y.; Iwasaki, S. Tetrahedron 1996, 52, 14543; Blokhin, A. V.; Yoo, H. D.; Geralds, R. S.; Nagle, D. G.; Gerwick, W. H.; Hamel, E. Mol. Pharmacol. 1995, 48, 523.
Critical issues, therefore, for further pharmaceutical development of any sufficiently active analog are increases in chemical stability, increases in hydrophilicity and improved availability versus the natural product. Curacin A is sensitive to oxidation, acids, and bases, and is readily, irreversibly absorbed into plastic containers such as polyethylene 96-well plates. Therefore, a need exists in the art for more efficient synthetic methods for producing curacin A analogs.
The present invention provides such methods. The present invention comprises the synthesis of 1-(un- and substituted aryl)-4-methyl-11-(heterocycle)undeca-4,6,10-trien-1-ols, and related compounds, and their preparation by a parallel and fluorous phase scheme. The lead compounds on which the idea for these agents was derived are structurally and synthetically complex antimitotic agents that suffer from physiochemical shortcomings (extreme hydrophobicity, easily oxidized to inactive species). The compounds of the present invention are both structurally and synthetically simpler and are not prone to oxidative inactivation. The compounds potently (in nanomolar concentrations) inhibit the growth of cultured human carcinoma cells, bind isolated tubulin and inhibit its assembly into microtubules in vitro, and cause mitotic block as determined by phosphorylation of histone H3 in human breast carcinoma cells.